1. Field of the Invention
The present invention relates to an analysis apparatus and an analysis method for analyzing a secondary battery during charging and discharging.
2. Description of Related Art
Lithium ion secondary batteries are used as power supply devices for electric vehicles, mobile terminals, and the like. Research and development for secondary batteries have been rapidly progressed. In the development of secondary battery products, it is a challenge to achieve an increase in capacity of secondary batteries and an improvement in performance, such as high-rate charging and discharging, so as to apply secondary batteries to electricity storage systems for electric vehicles and the like.
As a method of evaluating the performance of a secondary battery, a change in battery voltage during the cycle of charging and discharging is detected and the amount of electricity stored in the battery is detected, to thereby evaluate the performance based on these characteristic curves. For example, a method is known in which a change dV in voltage value and a change dQ in quantity of charged electricity are obtained using a charged electricity quantity Q and a battery voltage V of a secondary battery and an abnormal state of charge is detected from a Q-dV/dQ curve (for example, see Japanese Unexamined Patent Application Publication No. 2012-181976).
As another evaluation method, a method of evaluation based on an AC impedance is known (for example, see Japanese Unexamined Patent Application Publication No. 2009-97878). In such a known evaluation method, frequency characteristics of an internal impedance of a secondary battery are measured by an AC impedance method. Then, optimal values of parameters of components are determined so that the frequency characteristics of the internal impedance match the frequency characteristics of an impedance model including an equivalent circuit representing an electrochemical impedance of a positive electrode and a negative electrode.
As further another evaluation method, an evaluation method using X-ray diffractometry is known (for example, see Japanese Unexamined Patent Application Publication No. 2001-110419). In this evaluation method, powder X-ray diffraction measurement is performed on each cathode active material in an uncharged state. Cathode active materials having a value of a half-value width of a diffraction peak on a (003) lattice plane in the range from 0.095° to 0.130° are determined as non-defective products.
Since the evaluation method based on a charging and discharging curve and the evaluation method using an AC impedance as described above are electrical methods, output information is an average characteristic of the entire battery. Accordingly, these methods have a drawback that the non-uniformity of electrochemical reaction within the battery and the local reaction rate distribution cannot be evaluated. Furthermore, the evaluation method using the X-ray diffraction requires a device for producing powerful X-rays, resulting in the disadvantage of an increase in the size of an evaluation device.
On the other hand, in the development of secondary batteries, if a change with time of the internal structure of each battery, specifically, a change with time of active materials, can be observed from the outside as image information, it is expected to acquire useful development data. For example, the color and shape of cathode and anode active materials are assumed to change depending on the state of charge and the concentration of Li ions. Accordingly, if changes in color, shape, and size of the active materials can be recognized from the outside, the distribution state of Li in the cathode active material and the distribution state of Li in the anode active material layer can be recognized. Thus, it is expected to collect data useful for the development of new battery materials.
Further, by using image data, an image distribution within a second battery can be observed. Thus, there is an advantage of being able to observe a local change in a wide area. Furthermore, if data representing the charging and discharging characteristic and the color image characteristic of each secondary battery, which are temporally linked to each other, can be acquired, analysis data in which the electrical characteristic and the image characteristic are linked to each other can be acquired. This makes it possible to carry out a more useful data analysis.
It is an object of the present invention to provide an analysis apparatus and an analysis method which are capable of outputting various types of analysis data on a secondary battery.